Control of parasitic bronchitis and gastroenteritis in grazing cattle by strategic prophylaxis with ivermectin

In May 1985 four groups of 10 calves, aged between four and five months, were turned out on to separate, permanent pastures of equal area which had been seeded during the previous few days with larvae of Dictyocaulus viviparus. One group acted as a control, the second was vaccinated with lungworm vaccine before turnout and treated with thiabendazole three, eight and 13 weeks after turnout, while the third and fourth groups were given ivermectin three times (three, eight and 13 weeks after turnout) and twice (three and eight weeks after turnout), respectively. A severe outbreak of parasitic bronchitis resulted in the death of three control calves within five weeks of turnout and parasitic bronchitis and gastroenteritis affected the second group of calves after approximately four months at pasture. The calves given ivermectin excreted no lungworm larvae and remained free of clinical parasitism throughout the trial.     

Netobimin in drinking water for treatment of bovine parasitic bronchitis: a field experiment

Lungworm-infected seeder calves were used on four 1.41 ha paddocks to ensure that groups of 11 calves would be exposed to a heavy challenge with Dictyocaulus viviparus. By the 39th day after turnout there was a serious episode of respiratory disease and a diagnosis of parasitic bronchitis was confirmed by post mortem and faecal examination. One group of trial calves was treated with netobimin administered in the drinking water at 2.8 mg/kg/day for seven consecutive days; another group received the same treatment supplemented with flunixin meglumine at 2.2 mg/kg/day for three days; a third group was given a single oral dose of 7.5 mg netobimin/kg; only emergency treatments were given to calves in the control group. The clinical response to the drinking water treatments was highly satisfactory and better than the response to the single oral treatment.     

Effect of repeated doses of levamisole on grazing cattle infected with Dictyocaulus viviparus

Seventy-one worm-free Friesian calves were allocated by weight to three trial groups (1, 3 and 4) of 18 and a control group (2) of 17 animals. Calves in group 1 were vaccinated with a bovine lungworm oral vaccine on days 0 and 28, and on day 42 all groups were turned out to graze together on pasture known to be infected with Dictyocaulus viviparus larvae. Twenty-eight days after first exposure to infection one control calf died of parasitic bronchitis. Anthelmintic medication consisting of two doses of levamisole (7 . 5 mg/kg) at 14 day intervals was promptly administered to group 3 calves and three doses at the same intervals to group 4 calves. All calves were challenged with 20,000 infective D viviparus larvae on day 147. Calves were weighed every 14 days throughout the trial which ended 42 days after challenge. Pasture contamination and infectivity were monitored by pasture larval counts and tracer calves. Statistically there was no significant difference between the performances of treated and vaccinated groups before challenge but all were significantly superior to the control group. After challenge the productivity of all experimental groups was temporarily depressed but the levamisole treated cattle recovered more rapidly becoming significantly heavier than the vaccinates at the end of the trial. The mean group weight gains over the trial period were 89 . 92, 63 . 87, 88 . 67 and 98 . 70 kg in groups 1, 2, 3 and 4 respectively.     

Immunity to parasitic bronchitis of yearling cattle treated with ivermectin during their first grazing season

A group of 12 winter-born calves was divided into two groups of six. During the following summer one group grazed on pasture infected with Dictyocaulus viviparus, and was treated with ivermectin injections at three, eight and 13 weeks after turn out. The other group remained housed. Both groups were housed during the winter and then together with a group of younger calves were challenged with a trickle infection of D viviparus larvae at the rate of 25 third stage larvae/kg bodyweight for one month and then slaughtered. The group which had been exposed to previous infection was least affected by parasitic bronchitis and on the basis of serological titres and worm burdens had developed resistance to the challenge infection. The other older group was also more resistant than the younger calves.     

Patterns of parasitic nematode infection and immunity in dairy heifers treated with ivermectin in a sustained-release bolus formulation either at turnout or in the middle of the grazing season

Twenty-eight Holstein-Friesian heifers, born the previous year and weighing between 130 and 310 kg, were allocated to one of two treatment groups by restricted randomisation, based on their initial weight. The heifers in group 1 were each treated with ivermectin in a sustained-release bolus formulation at turnout in April, and those in group 2 were each given an ivermectin bolus on July 10, 84 days after turnout. On that day the mean geometric worm egg counts of groups 1 and 2 were 0.4/g and 38.8/g, respectively, and they both had a mean plasma pepsinogen concentration of 0.59 iu/litre; in group 1, two of 14 faecal samples were positive for Dictyocaulus viviparus larvae, and in group 2 all 13 samples were positive; in group 1 eight calves were positive and three inconclusive for the presence of antibodies to D viviparus, and in group 2 the corresponding figures were 10 positive and two inconclusive; the mean liveweights of groups 1 and 2 were 274.4 kg and 262.8 kg, respectively. By December 4,231 days after turnout, the corresponding results were: mean geometric worm egg counts of 2.2/g and 0.5/g; one of 13 and none of 14 faecal samples positive for D viviparus larvae; 12 positive and two inconclusive and none positive and 10 inconclusive for the presence of antibodies to D viviparus; 214 days after turnout their mean liveweights were 361.1 kg and 358.3 kg. Although the patterns of parasitic nematode infection were different in the two groups during the grazing season, by the time they were housed both groups had achieved similar liveweights and showed evidence of an immune response to both D viviparus and gastrointestinal nematodes.     

Failure to eradicate the lungworm Dictyocaulus viviparus on dairy farms by a single mass-treatment before turnout

On two dairy farms it was attempted to eradicate lungworm, Dictyocaulus viviparus, by means of a single mass-treatment of all cattle that had been grazed the previous year(s), before turnout in the spring. Both farms experienced two years of lungworm outbreaks in the adult dairy herd prior to this study. Following confirmation that both herds contained lungworm carriers, all animals older than approximately 6 months were treated with eprinomectin in March 2007. One week after treatment none of the animals were shedding lungworm larvae. Subsequently, animals were pastured according to normal farm routine. From August to November all first-calving heifers were coprologically and serologically monitored for lungworm infection. During 2007 both farms remained lungworm-negative and did not report any clinical sign indicative for a lungworm infection. The following year, on one of the farms replacements grazing on cow pastures, started showing signs of parasitic bronchitis which was serologically confirmed. The other herd remained free of parasitic bronchitis until at least the fourth year after the mass treatment, although some coughing was noticed in 2008 among first-lactation heifers. It was concluded that a single mass-treatment before the grazing season may be useful to break a series of annual lungworm outbreaks. However, it is not a secure method to prevent parasitic bronchitis for more than one year.     

Field evaluation of a method for the chemoprophylaxis of parasitic bronchitis in calves

Studies on the epidemiology of Dictyocaulus viviparus infections in Denmark have suggested that the adult lungworms present in calves around the sixth week after turnout play an important role in determining the subsequent pattern of disease. This trial was designed to test whether prophylactic treatment at this time would control disease in calves kept under British conditions. Thirty autumn-born Friesian or Friesian-cross bull calves were allowed to graze the whole of a 5 hectare field for six weeks after turnout. The field was then divided into two and the calves split into matching groups, one group being put into each of the paddocks. One group was treated with levamisole at this time and again two weeks later while the other was kept as an untreated control. Anthelmintic treatment resulted in a marked reduction in larval excretion and considerably delayed the build-up of infection on pasture. This in turn delayed the onset and reduced the severity of clinical signs in the treated group. However, as disease was not eliminated completely this prophylactic programme cannot be recommended to the British farmer in its present form. These findings are discussed in the context of the yet incomplete knowledge of the epidemiology of parasitic bronchitis.     

Studies on the epidemiology of bovine parasitic bronchitis.

In the West of Scotland the epidemiology of parasitic bronchitis in grazing calves was studied over a two year period with the aid of tracer calves and herbage examinations for Dictyocaulus viviparus larvae. The observations of both years emphasised the importance of overwintered lungworm larvae as a source of disease. In the first year it was shown that the ingestion and development of these overwintered larvae were, by themselves, directly responsible for severe morbidity, high faecal larval counts and deaths. In the second year it was shown that pasture ungrazed during the winter and spring and from which a hay crop was removed in mid-summer was still capable of producing clinical parasitic bronchitis in susceptible calves within three to four weeks of their introduction in later summer. In both years there was some evidence that the outbreaks appeared to be associated with the sudden availability of infective larvae on the herbage. The possibility that such larvae may have survived for many months in the soil is discussed. Despite the heavy challenge with lungworm larvae experienced by the grazing calves in the first year those vaccinated with lungworm vaccine survived, their clinical signs were mild and of short duration and their faecal larval output was greatly reduced.     

Oxfendazole pulse release intraruminal devices and bovine parasitic bronchitis: comparison of two control strategies in a field experiment

Lungworm-infected seeder calves were used on two 1.41 ha paddocks to ensure that groups of 11 susceptible trial calves would be exposed to heavy early season challenge with Dictyocaulus viviparus. This produced conditions for an artificially severe test of two control strategies. The first employed a front-loaded oxfendazole pulse release bolus, ie, an intraruminal device which released one therapeutic anthelmintic dose immediately and five subsequent pulses at approximately three-weekly intervals. These front-loaded boluses were given to five of 11 calves on one paddock as soon as parasitic bronchitis had become clinically obvious (34 days after turnout) while the remaining six calves were kept as untreated controls. Clinical signs quickly subsided in the treated animals and no further respiratory problems occurred despite continued exposure to reinfection. The other control strategy involved the administration at turnout of an oxfendazole pulse release device which released the first of five anthelmintic doses approximately three weeks after administration, to all 11 calves on the other paddock. This strategy was almost completely successful in preventing patent infections from establishing and reduced the infectivity of the pasture in August and September by 94.1 per cent as shown by tracer calf studies. The calves treated at turnout performed better than the calves treated with the front-loaded boluses for most of the season and had an average weight-gain advantage of 20.4 kg at housing (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Control of naturally acquired bovine parasitic bronchitis and gastroenteritis with an oxfendazole pulse release device

Four groups, each of six male Friesian calves, were set-stocked on separate 0.66 ha paddocks from May 7 until October 23 1986. Each of the animals in groups 1 and 4 was dosed with an oxfendazole pulse release bolus at turn out whereas the animals in groups 2 and 3 were left untreated. Parasite-free naive tracer calves were introduced into each paddock for a limited period 12 days after turn out and again at the end of the trial. No adverse reactions or clinical signs were observed in either of the groups of calves which received boluses. The development of clinical parasitic gastroenteritis in both the untreated groups necessitated the humane slaughter of two animals and emergency anthelmintic treatment of the remainder. The lower plasma pepsinogen concentrations, and lower faecal egg and larval counts and worm burdens post mortem, together with the absence of clinical signs of parasitic gastroenteritis and bronchitis in the treated calves, confirmed the high efficacy of the bolus treatment.     

Effect of ivermectin and oxfendazole on shedding of larvae of the lungworm (Dictyocaulus viviparus) by red deer (Cervus elaphus)

Thirty eight newly weaned hinds were randomly allocated to one of two equal groups. One group received ivermectin, the other, oxfendazole at dose rates of 0.2 mg/kg and 4.5 mg/kg, respectively. All deer were drenched four times and were grazed on pasture. Both anthelmintics reduced D. viviparus faecal larval counts to low levels 20 days after dosing, but the mean larval output and the proportion of deer shedding D. viviparus larvae at 27 and 33 days after treatment, were significantly lower in the ivermectin treated group. There was no significant difference in weight gain between the two groups throughout the trial. This study suggests that ivermectin prevents reinfection with D. viviparus for approximately 14 days longer than oxfendazole.     

Observations on the epidemiology of Dictyocaulus viviparus in north west England

A five year ley pasture was used as a source of natural infection with Dictyocaulus viviparus for cattle in anthelmintic trials. Pasture larval counts, faecal larval counts of permanently grazing calves and lungworm burdens harboured by tracer calves were monitored in three grazing seasons to assess the pattern of infection. Carrier calves were introduced at the beginning of the grazing season in the first two years of the study but not in the third. In the fourth year the pasture was subdivided into two paddocks where overwintered infection with and without carrier infection were compared. A control paddock exposed to carrier infection but no overwintered infection was also monitored. Pasture larvae survived the winter but carrier infection appeared to make a larger contribution to pasture larval counts and the onset of parasitic bronchitis in susceptible calves. In the absence of grazing cattle at the end of the grazing season the concentration of D viviparus larvae on the herbage fell rapidly to undetectable levels. Discrepancies between contamination of herbage by infective D viviparus larvae and infectivity of pasture for susceptible cattle occurred in all years but were particularly marked on the third year when natural immunity appeared to influence the number of lungworms accumulating in tracer calves. Failure to recover lung worms from tracer calves cannot be regarded as an accurate indication of lungworm free pasture. In the first three years the proportion of the lungworm population which was inhibited in tracer calves was higher early and late in the grazing season and negligible in mid season. This suggests that a predisposition to inhibition in larvae which have overwintered on pasture may influence the time of onset of parasitic bronchitis in the next grazing season, but results from the fourth year did not support this hypothesis.     

Comparative study of early-season prophylaxis using ivermectin with lungworm vaccination in the control of parasitic bronchitis and gastroenteritis in cattle

Twenty-four first-season calves were randomly allocated to three similar groups (1-non-treated controls; 2 - vaccinated against lungworm; 3 - treated with ivermectin 21, 56 and 91 days after turnout) and set-stocked on separate pastures. Parasitic bronchitis became evident in the controls and signs of parasitic gastroenteritis were seen later in the vaccinates, but the ivermectin-treated calves remained healthy. After autumn housing, all were kept as a single group for the winter. The following summer, six of the ivermectin-treated animals and their matching vaccinates were grazed together, without further prophylaxis, along with six first-season calves. The latter displayed evidence of mild but debilitating pulmonary and gastrointestinal parasitic disease while both groups of yearlings remained healthy (with the exception of one diarrhoeic vaccinate). Thus, the immune status of the ivermectin-treated animals appeared to be comparable to that of the vaccinates. This conclusion was supported by parasitological observations and by artificial challenge at the end of the second grazing season.     

Pasture study of two types of oxfendazole pulse release bolus for controlling nematodes in calves

One group of first-season calves was dosed with an oxfendazole pulse release bolus at spring turnout (April 30) and on July 15 a second group received the front-loaded oxfendazole pulse release bolus. The objective was to test the boluses for the prophylaxis or control of nematodiasis. The control group consisted of calves to which no bolus was administered. The three groups occupied separate but adjacent plots. For the first five weeks of the trial, three calves, artificially infected with Dictyocaulus viviparus grazed in each plot. Parasitic bronchitis severely affected the control calves, necessitating repeated emergency treatment, whereas administration of the bolus at turnout almost completely prevented this condition. D viviparus infection increased markedly on the control herbage in July and August but was eliminated by the end of June on pasture grazed by bolus treated calves. Treatment in mid-season with the front-loaded bolus brought an outbreak of parasitic bronchitis under control. Gastrointestinal worm egg output was satisfactorily suppressed after the administration of both boluses, resulting in reduced levels of herbage infection. Calves treated with a bolus at turnout gained significantly more weight than either the controls (P less than 0.001) or the calves treated with a front-loaded bolus in mid-season (P less than 0.01). The weight-gain of the calves treated with a front-loaded bolus was slightly but not significantly greater than that of the control calves. On the basis of faecal egg counts, the first pulse released from the standard boluses was delayed and one front-loaded bolus failed to release a dose.(ABSTRACT TRUNCATED AT 250 WORDS)     

The residual effect of treatment with ivermectin after experimental reinfection with nematodes in calves

The residual effect of treatment with ivermectin after experimental reinfection in calves was tested. Twenty-four calves were divided into 6 groups of 4 calves each. All calves received a primary infection of 50,000 larvae of both Ostertagia ostertagi and Cooperia oncophora and 1000 Dictyocaulus viviparus larvae. Calves of group 1 remained untreated, and all other calves were treated 21 days after primary infection (0.2 mg/kg injected subcutaneously). Calves of groups 1 and 2 were slaughtered 7 days later. Calves of groups 3-6 were reinfected with the same number of larvae 3 days, 1, 3 and 6 weeks after treatment respectively. Slaughter was 21 days after reinfection. Based on post-mortem worm counts the efficacy of ivermectin after primary infection was 99.7% for O. ostertagi, 95.1% for C. oncophora and 100% for D. viviparus. A residual effect was present for at least one week, but could not be observed 3 weeks after treatment.     

A comparison of interactions between vaccination against Dictyocaulus viviparus and anthelmintic suppression in immunised and unimmunised yearling cattle

Twenty parasite-naive calves aged approximately four months were divided randomly into four groups of five. Two groups were treated with oral lungworm vaccine. One immunised group plus another non-immunised group were put out to graze on May 1 on a pasture known to be contaminated with Dictyocaulus viviparus infective larvae during the previous autumn. All the calves both indoor and outdoor were treated with ivermectin at three, eight and 13 weeks after the first groups started to graze and again at housing at the end of September. After the winter housing period on April 27 of the following year all the calves were given an artificial challenge of D viviparus infective larvae at the rate of 15 larvae per kg bodyweight, and the clinical and parasitological reactions monitored. All the calves which had been vaccinated or exposed to field infection during year 1 reacted strongly in ELISAs using antigen prepared from fourth stage D viviparus larvae but much less strongly in similar tests using adult derived antigen. Clinically those calves exposed to previous field infections were less severely affected than the housed calves, although parasitologically all three groups with prior exposure to D viviparus appeared to have a similar functional level of immunity to the challenge infection in comparison to the unexposed calves of the same age.     

Concurrent use of the oxfendazole pulse release bolus and the monensin rumen delivery device in young grazing cattle

When they were turned out to grass in May 1987 for their first season, 10 calves were dosed with a 5 x 750 mg oxfendazole pulse release bolus (OPRB) and a monensin sodium rumen delivery device (RDD); eight calves received one OPRB; 10 calves received one RDD and eight calves received neither bolus. Each group was set-stocked on individual paddocks which had been grazed during the previous season by cattle which developed clinical parasitic gastroenteritis and bronchitis (husk). In July, before they were due to be moved to new pastures in mid-summer, and before they were dosed strategically with levamisole HCl, some of the calves not dosed with an OPRB succumbed to clinical parasitic gastroenteritis and husk and received emergency anthelmintic treatment, after which no further clinical episodes occurred. The 'dose and move' strategy was implemented in early August after which both groups not dosed with an OPRB were set-stocked together until the trial ended on October 14, 147 days after turn out. The two groups of calves which had received the OPRB were also moved to new pasture and set-stocked together until the end of the trial. No evidence of clinical helminthiases developed in either of the two groups of calves dosed with OPRBs and their faecal worm egg and larval counts, and plasma pepsinogen activities remained low. They gained significantly more weight than the two groups of calves not dosed with OPRBs (P less than 0.001). The bolus types were compatible and induced no untoward side-effects when used together.     

Comparison of a levamisole sustained-release bolus and ivermectin treatment to prevent bovine lungworm infection

The efficacy of a levamisole sustained-release bolus to prevent parasitic bronchitis in calves in their first grazing season was compared to ivermectin treatment at three, eight and thirteen weeks after turn out. Contamination of the pasture was established by experimentally infected seeder calves. Twenty calves were split into two groups. Ten calves of one group received a bolus at the start of the experiment. In the other group the calves were treated with ivermectin at 21, 56 and 91 days. Two principal calves from each group were killed during the experiment to study histopathological changes. Pairs of tracer calves were introduced on both pastures at intervals of four weeks throughout the grazing period. The permanent calves were challenged with lungworm larvae at housing and slaughtered four weeks later. Both systems prevented parasitic bronchitis. Larval output was completely reduced in the ivermectin-treated calves while all bolus-treated calves excreted larvae at certain times. The highest group average was 4 larvae per gram faeces. Eosinophilia, ELISA-titres and histopathological changes confirmed the differences in larval uptake. Challenge infection was not successful in either group and no worms were found at slaughter. Weight gain was significantly different at housing in favour of the ivermectin-treated calves, but after challenge this was reduced due to a higher weight gain in the bolus-treated calves. The practical consequences of the results have been discussed.     

Comparison of the efficacy of dermal formulations of ivermectin and levamisole for the treatment and prevention of Dictyocaulus viviparus infection in cattle

Four groups of six parasite-naive calves were infected at seven day intervals with three doses of infective larvae of Dictyocaulus viviparus. Twenty-one days after the first dose three of the groups were treated either with an injectable formulation of ivermectin at a dose rate of 200 micrograms/kg bodyweight, or with pour-on preparations of levamisole at 10 mg/kg or ivermectin at 500 micrograms/kg. On day 28 two calves from each group were slaughtered and their burdens of lungworms counted. On day 35 the remaining calves were reinfected with D viviparus infective larvae at a rate of 80 L3/kg. The levamisole preparation was 94.6 per cent effective and both ivermectin preparations were 100 per cent effective against the initial infections. The ivermectin-treated calves were protected from the reinfection which subsequently became patent in the levamisole-treated and control calves.     

Anthelmintic activities of ivermectin against immature and adult Dictyocaulus viviparus

Eighteen calves about 3 months old were inoculated with 3,000 Dictyocaulus viviparus infective larvae. Three groups of 6 calves each were formed. Thirteen days after inoculations, 3 of the 6 group 1 control calves were given vehicle subcutaneously (SC) and the group 2 calves were given ivermectin at the dose rate of 200 micrograms/kg, SC. Thirty-five days after inoculation, the remaining 3 calves in group 1 were given vehicle SC and the group 3 calves were given ivermectin at the dose rate of 200 micrograms/kg, SC. Necropsies were performed 42 days after inoculations. A total of 474 D viviparus was recovered from the group 1 control calves, whereas none was recovered from the calves treated when the nematodes were in the 4th stage of development (group 2) or adult stage (group 3).